1. Field of the Invention
The present invention relates to a ceramic heater suitable for ensuring a uniform temperature distribution for treating semiconductor wafers, substrates for liquid crystals, etc. More specifically, it relates to a circuit pattern of resistance heating elements embedded in an insulating substrate and to a substrate-treating apparatus incorporating an insulating substrate in which resistance heating elements having the circuit pattern are embedded.
2. Description of the Background Art
Layer formation and etching treatment are performed on a semiconductor wafer or a substrate for liquid crystals by using the chemical vapor deposition (CVD), physical vapor deposition (PVD), or sputtering method. Ceramic heaters have been used to support these objects to be treated such as wafers and substrates and to heat them to a specified treating temperature. In recent years, these ceramic heaters have been increasingly used in a treating apparatus equipped with a vacuum chamber.
The published Japanese utility-model application Jitsukaihei 2-56443 has disclosed a ceramic heater 100 shown in FIG. 7. The ceramic heater 100 has a function of an electrostatic chuck that holds an object to be treated such as a semiconductor wafer. The ceramic heater comprises laminated circular insulating substrates 101a and 101b, a resistance heating element 102 embedded between the two substrates, a laminated dielectric layer 104, and an electrode layer 103 embedded between the substrate 101b and the dielectric layer 104. FIG. 8 shows a circuit pattern 200 of the resistance heating element 102. A current-receiving point 102a and a current-releasing point 102b are provided in the peripheral area of the insulating substrate 101. These points are connected to terminals 102c that penetrate through the insulating substrate 101a (see FIG. 7).
An object 105 to be treated such as a semiconductor wafer is attracted to and held on a supporting surface 106 by applying a voltage to the electrode layer 103 from another terminal, which is separately provided. An electric current is supplied from the terminals 102c to the resistance heating element 102 to heat the object 105 to be heated to a specified treating temperature.
According to this utility model, the electrostatic chuck 100 can function as a heating device and transfer the heat effectively to the semiconductor wafer. Because no ancillary device such as a conventional heating device is required, the electrostatic chuck 100 can be simplified and the cost reduction can be achieved.
The published Japanese patent application Tokukaihei 11-317283 has disclosed a circuit pattern that is composed of at least two linear resistance heating elements connected in parallel, instead of the above-described single resistance heating element 102. The disclosed invention intends to improve the temperature distribution of a ceramic heater in order to adapt to the upsizing of semiconductor wafers. To achieve this object, the resistance heating elements are divided into a multitude of groups in the longitudinal direction to measure the cross-sectional areas of the resistance heating elements belonging to individual groups. Some of the linear resistance heating elements constituting the groups having large cross-sectional areas with reference to the group having the minimum cross-sectional area are removed in order to equalize the resistance.
On the other hand, recent years have seen the advancement in the upsizing of semiconductor wafers from the initial diameter of about 6 inches to the upsized diameter of 12 inches. As a result, ceramic heaters are required to have the capability of highly uniformly heating the entire surface of the large-area semiconductor wafer. In addition, the treating temperature has increased from the initial temperature of about 400xc2x0 C. to the recent high temperature exceeding 550xc2x0 C. At present, it is required to reduce the temperature variations on the supporting surface of the ceramic heater to at most xc2x11%. However, with the above-described prior arts, the temperature distribution on the entire surface of the upsized semiconductor wafer cannot be equalized within the required limit.
An object of the present invention is to offer a technology that achieves a highly uniform temperature distribution on the surface of large-area semiconductor wafers and substrates for liquid crystals without prior measurement of the resistance-heating-element circuit and subsequent adjustment of the value of the resistance. Another object of the present invention is to offer a substrate-treating apparatus incorporating the above-mentioned technology.
At least one current-receiving point and at least one current-releasing point are provided at the central portion of an insulating substrate of a ceramic heater. One or more resistance-heating-element circuits are embedded in the insulating substrate spirally or pseudospirally from the central portion including the current-receiving point to the peripheral portion of the insulating substrate. All the circuits merge with one another at the outermost portion. One or more resistance-heating-element circuits are separated at the outermost portion of the resistance-heating-element circuits and are formed spirally or pseudospirally from the outermost portion to the central portion including the current-releasing point.
When at least two current-receiving points, at least two current-releasing points, or both are provided, a more distributed circuit pattern of resistance heating elements can be formed.
The above-described circuit pattern is formed such that the resistance-heating-element circuit formed from the central portion including the current-receiving point to the peripheral portion of the insulating substrate alternates with the resistance-heating-element circuit separated at the outermost portion of the resistance-heating-element circuits and formed from the outermost portion to the central portion including the current-releasing point. This formation can eliminate the effects of the magnetic fields generated by the electric currents flowing in the resistance-heating-element circuits, improving the temperature distribution. Therefore, even large-area semiconductor wafers and substrates for liquid crystals can be heated highly uniformly and stably at high treating temperatures.
When an insulating substrate provided with resistance heating elements having the circuit pattern described above is used for a ceramic heater in an apparatus for treating semiconductor wafers or substrates for liquid crystals, a large-diameter object can be heated on the insulating substrate with a highly uniform temperature distribution. In other words, layer formation and etching treatment are performed on a semiconductor wafer or a substrate for liquid crystals with stability and high precision by using the CVD, PVD, or sputtering method.